Microencapsulation is a process for completely enveloping tiny masses of solid particles, or liquid droplets in a protective coating which separates the substance from its environment. The use of microencapsulated chemicals for toxicology studies presents a number of advantages, i.e. it permits testing volatile or chemically reactive compounds in the animal diet, minimizes problems with palatability, etc. Volatile and/or reactive chemicals have been encapsulated using a gum/sorbitol matrix and determined to be stable when mixed with rodent feed. Relative bioavailability of the microencapsulated trichloroethylene compared to the neat test material indicates no significant difference in absorption after oral administration. Feeding studies using the microencapsulated trichloroethylene are planned.